I recently up-voted a savvy comment which implied that the OP should take a fresh look at his question. Then I noticed that there were more, currently hidden, comments. Only after I clicked to reveal these was it was apparent that the OP had already taken the savvy comment on board, and so there was no point in up-voting it. My question is: why not just show all the comments in the first place? You need to see them all to assess how to respond to them, in any case.
There has to be some limit on how many comments are shown. The site shows $n$ most voted comments, not $n$ first or most recent, with the idea that the comments worth showing are those that make important observations about the post. This design is also meant to suppress discussion threads consisting of comments replying to other comments replying to other comments. If you need to see other comments to understand the meaning of a comment, that probably means the thread needs a clean-up (in your case, that savvy comment should have been deleted as obsolete).
Another benefit of limiting the number of comments is technical: it keeps the HTML source of the page short and focused on the actual question & answers. This helps search engines better "understand" what the page is about, without being confused by tangential remarks. SE lives and dies by its Google page rank.
You can also read Jeff Atwood's explanation at Comments: Top n Shown
(For the record, $n=5$ on main site and $n=15$ on meta sites.)